This invention relates to thiols and more particularly to ferrocenyl thiols.
Unsaturated polymers such as polybutadienes and polyurethanes are frequently used as propellant binders. Ferrocene has frequently been used as a burning rate modifier in those propellants. Ferrocene, however, tends to migrate within the propellants, resulting in an uneven distribution of ferrocene and thus uneven burning of the propellant. This problem will be eliminated if the ferrocene is bound in some way to the polymer backbone of the propellant binder.
Thiols readily enter into free radical addition reactions with olefins to produce stable products. See for example Organic Reactions, volume 13, (John Wiley and Sons, Inc., New York, 1963) pp. 165-190. The free radical addition of ferrocenyl thiols to the carbon-carbon double bonds of the polymers is one method by which the ferrocenyl group can be bound to the polymer.
G. R. Knox and P. L. Paulson (J. Chem. Soc. 1958, p. 692) demonstrated that ferrocene thiol can be prepared in three steps from ferrocene, via sulfonation, conversion of the resultant monosulfonyl chloride with lithium aluminum hydride. They reported that the thiol could never be obtained completely pure because of the extreme ease with which it was oxidized to the corresponding diferrocenyl disulfide. Another problem is that steric hinderance makes it more difficult to introduce ferrocene thiol in a polymer backbone.